1. Field of the Invention
The present invention relates to a method for manufacturing a heating element having a coating layer of catalyst or the like, and electronic dust collector using said heating element, and an air conditioner provided therewith. Especially, the invention relates to a technique for forming a ceramic catalyst layer on a sheathed heater simply and at low cost.
2. Description of the Prior Art
Hitherto, there has been known, as an example of a heating element provided with a coating layer such as a catalyst, as shown for example in Japanese Laid-open Patent Publication No. HEI 9-61042, one made by coating a surface of a glass tube heater (sheathed heater) self-containing an electric resistor with a catalyst coating layer. Further, there is known, as shown for example in Japanese Laid-open Patent Publication No. HEI 8-41655, one made by providing an aluminized steel, coating the surface thereof with a glass coating, firing, and further forming a catalyst coating layer on its surface.
By the way, the coating of a catalyst or the like in the heating element is formed through a baking treatment in a high temperature furnace. The sheathed heater as a heater material is made by filling an electric resistor line, magnesium oxide, etc. in a metal tube, and sealing both ends of the metal tube. Accordingly, the glass sealed port parts require to be immune from thermal destruction. Thus, according to the conventional method of manufacturing the heating element for forming a catalyst coated layer on the metal tube surface of the sheathed heater, there has been practiced, prior to sealing with glass the metal tube of the sheathed heater, to provide the metal tube surface with a catalyst or the like by baking, followed by inserting a filler in the metal tube and then providing glass sealing. Also, in the one made by using a metal tube of a piece independent from the metal tube of the sheathed heater, a metal tube of a separate piece is put in a furnace, a catalyst coated layer is fired on the tube surface, and a metal tube provided with firing of the catalyst layer is fixed to the metal tube of the sheathed heater by caulking.
However, in case of the method for manufacturing the heating element with a catalyst layer as described above, a baking treatment using a high temperature furnace is required for forming a catalyst layer, for which purpose a large scale equipment is required, and there is a problem of difficulty to manufacture a heating element simply at a low cost. Furthermore, in the method of forming a catalyst layer directly on the surface of the metal tube of the sheathed heater, the completed sheathed heater cannot be used, because of which the manufacturing steps are increased, leading to a cost increase.